Lens and method of making same



Nov; 29, 1938. F. D. KENNEY LENS AND METHOD OF MAKING SAME OriginalFiled June 6, 1955 I v 2 Sheets-Sheet l P112171v H6117 FlliI FEE H511f'llim Hlifl F1511 F151 F171 Ham P/ZUZF INVENTOR Y Fa] h'nney F. D.KINNEY Nov. Z9,v 1938.

LENS AND METHOD OF MAKING SAME Original Filed June 6, 1955 2Sheets-Sheet 2 F1512 Fllilfl Ham HEM INVEIJTOR BY fzy 2 19/17/29 AT NEYReissued Nov. 29, 1938 UNITED STATES LENS AND METHOD OF MAKING SAltIEFay D. Kinney, Southbridge, Mass, assignor to American Optical Company,Southbridge,

Mass., a voluntary association of Massachusetts Original No. 2,067,194,

dated January 12, 1937,

Serial No. 25,225, June 6, 1935. Application for reissue September 1,

7 Claims.

This invention relates to improvements in bifocal or multifocal lensesand has particular reference to an improved blank therefor and themethod of making the same.

A principal object of the invention is to provide improved means andmethod of making bifocal or multifocal lenses and to reduce considerablythe cost of production for the blanks of such lenses.

Another object of the invention is to provide an improved and lessexpensive method of fusing together multiple parts of the segment orbutton of such lenses where the line of jointure between the parts is ofan irregular nature as contrasted with a division line having a singlecontinuous line of jointure.

Another object of the invention is to provide means by which the joininglines of the segment or button parts may be finished for fusing in amore simple and less expensive manner than has been employed hitherto.

Another object of the invention is to provide an improved and lessexpensive method. of producing a two part button or segment for lensesof this character wherein is provided means of producing a finishedsegment having a lower por-- tion of circular outline and a transverseupper edge and an arcuate fillet at the junction of top and bottomedges.

Another object of the invention is to produce a button or segment forlenses of this character which will produce a finished segment with alower portion of circular outline and of a knife edge thickness alongthis circular outline.

Another object is to provide a novel method for making a bifocal ormultifocal lens blank having a reading segment with a transverse upperportion, a circular lower portion and fillets connecting said transverseand circular portions which is less expensive than methods heretoforeemployed.

Another object is to produce a bifocal or multifocal lens having areading segment in which a portion of the contour of the finished blankis preformed and in which the remainder is formed by forming the basecurve on the blank.

Another object is to provide a novel method of making a bifocal ormultifocal lens blank having a reading segment which has a preformedupper portion with depending terminal portions, the remainder of theportions being formed by the intersection of the curve of thecountersink of the major blank and the finished surface on one side ofthe blank and the depending portions 1938, Serial No. 228,001

servingas datum lines for determining the depth and position of saidfinished surface.

Another object is to provide a bifocal or multifocal lens having areading segment having a preformed transverse upper portion with filletsdepending therefrom and a lower circular portion formed by theintersection of the countersink curve for the reading segment and thebase curve formed on the finished lens blank, said fillet portionsserving as datum points with respect to Which the upper extremities ofthe circular portion may be aligned during the formation of the basecurve on the blank in order to properly locate said base curve on saidblank and control the depth to which the base curve is formed.

0ther objects and advantages of the invention will become apparent fromthe following description taken in connection with the accompanyingdrawings. It is apparent that many changes in the details ofconstruction and arrangement of parts and in the steps of the processmay be made without departing from the spirit of the invention asexpressed in the accompanying claims. It is therefore not desired tolimit the invention to the exact details and arrangement shown anddescribed as the preferred forms only have been shown and described byway of illustration.

Referring to the drawings:

Fig. I is a front view of a finished lens blank embodying the invention;

Fig. 11 is a cross section on line IIII of Fig. I;

Fig. III is a front view of the bottom of the button or segment;

Fig. IV is an end view of Fig. III;

Fig. V is a front view of the top part of the button or segment;

Fig. VI is an end view of Fig. V;

Fig. VII is a front view of the bottom of the button or segment with thediaphragm removed;

Fig. VIII is an end view of Fig. VII;

Fig. IX is a. front view of the top of the button or segment with thediaphragm removed;

Fig. X is an end view of Fig. IX;

Fig. In is a front view of the top and bottom of the segment or buttonfitted and secured together;

' Fig. XII is an end view of Fig. XI;

Fig. XIII is a front view of the top and bottom of the button or segmentsecured together and one face finished to fit the countersink of themajor blank;

Fig. XIV is an end view of Fig. XIII;

Fig. XV is a front view of the major blank with the countersink therein;

Fig. XVI is a cross section on line XVI-XVI of Fig. XV;

Fig. XVII is a front view of the complete button or segment secured inplace on the major blank;

Fig. XVIII is a cross section on line XVIII- XVIII of Fig. XVII;

Fig. XIX is a cross section of the complete lens blank in place on afusing block;

Fig. XX is a view showing a modification of the manner in which theparts of the button fit together;

Fig. )QII is a cross section of the button illustrated in Figs. XI andXII showing the method of supporting the parts in place on a fusingblock;

Fig. XXII is an elevational view showing a modification of the parts ofthe button; and

Fig. XXIII is a side view showing the. parts of the button interfittedwith the diaphragms left on for the fusing operation.

Recent development in the optical trade has brought about a great demandfor bifocal or multifocal lenses having a reading segment formed with atransverse upper portion, an arcuate lower portion with or withoutarcuate fillets connecting the arcuate portion and the transverseportion, such as shown in Fig. I. Practically speaking, it has been verydiflicult and expensive to produce a reading segment of such shape. Twomethods have been used heretofore and both methods are very expensive.With my invention such a reading segment can be produced at a much lowercost than heretofore.

Prior to this invention. it has been the practice to make the segment orbutton of lenses of this nature either by piercing ahole through onepart of the button and inserting the other part therein, or by makingthe button in three parts and securing them together. In the prior artstructures of this nature, the size and shape of the segment of thefinished lens was predetermined by the size and shape of the hole or bythe shape of the engaging edges of a plurality of pieces of glass whichwhen assembled and fused would produce the finished contour of thereading segment. In both of these prior methods it was essential tofinish the entire edge surfaces prior to the edge fusing operation. Thiswas not only an expensive procedure but much difficulty was encounteredin obtaining smooth and usable edge surfaces and in obtaining opticallyperfect fusion edges throughout the contour of the reading segments.

Another difficulty with structures of these types was that of reducingthe reading segment to a feather-like edge throughout the lower portionthereof as the operator during the abrading operation could notdefinitely determine whether or not the proper depth had been reached.In many instances a thick edge was allowed to remain throughout theentire contour of the finished segment which was objectionable becauseit was visible and cast annoying reflections. Such reflections would notexist if the lower contour was reduced to a feather type edge.

It is a principal object of this invention therefore to avoid'thesedifficulties and to reduce the cost involved by providing a portion ofthe contour of the segment with a preshaped shouldered transverse edgeproduced by edge fused surfaces which could be easily formed and theremainder of the contour with a feather type edge produced by theintersection of two curved surfaces, i. e. the countersink curve and thebase curve of the lens. The shouldered transverse edge being providedwith depending end-portions or fillets-with which the upper extremitiesof the lower curved edge of the segment are aligned to complete theshape of the segment. This controls the width and size of the finishedreading segment of the lens. The depending ends or fillets providedefinite gauge means by which the position and depth of the base curveof the lens may be easily controlled during the abrading operations.

Referring to the drawings wherein like reference characters denote likeparts throughout, the major part of the lens as shown in Fig. XV is madein the usual prior art manner by making the countersink depression I ina glass blank 2. This countersink l is usually spherical and has afinished optical surface. The material of the blank 2 is preferably theusual optical crown glass with a desired index of refraction. This blank2 may be of any color desired, of any required index of refractioncoefficient of expansion, coefficient of dispersion, melting point, etc.and may possess any of the characteristics usual with lenses of thischaracter.

The segment or button part, as shown in Fig. XIII, is made of two parts.The upper part 3 has preferably the same index of refraction as themajor blank 2. The lower part 4- has a different index of refraction.The part 3 is preferably the same crown glass as the blank 2. The part 4is preferably made of a barium crown glass or of flint glass of adifferent index from the part 3. The part 4 when made of barium crownglass, as is well known in the art, will reduce color defects becauseits dispersion is so related to the dispersion of the parts 3 and 2 asto produce a no color effect in the dispersion. It also has a lowermelting point than the part 3. When made of flint glass the part 4 has alower melting point than the part 3 but there will be color defects dueto the fact that there is a difference in the dispersion from that ofthe part 3.

During the pressing operation on the parts 3 and 4 of the segment, anoverflow must be provided and allowing the formation of the diaphragm 5accomplishes this result. Also during fusion of the parts 3 and 4, thediaphragms may be used to prevent a distorted line of fusion. In suchcase, the diaphragms would, of course, be ground off after the fusion ofthe parts of the segment.

The part 3 is pressed under heat in a manner similar .to that of thepart 4 and also has the diaphragm 5 for the same reason. The parts 3 and4 may be formed by using a. forming tool or any other device known tothe prior art, if desired. The contacting edges 6 and I may besandblasted if desired or may be finished in any manner known to theprior art.

I next fit the two parts 3 and 4 together, as shown in Fig. XI, andpreferably fuse them together. To fuse the parts together, I place themon a refractory block I9, see Fig. XXI. This block is inclined. The part4 which has the lower melting point is placed above the part 3 so thatwhen heat is applied the part 4 softens first and runs down by gravityto unite with the part 3. As clearly shown in Figs. IV and VIII, theedge 6 may be beveled slightly so that when the parts 3 and 4 fittogether the edge, of the surface I of the part 4 adjacent the fusingblock will contact the part 3 on this edge leaving a Wedge shapedclearance between the parts. Thus during fusion the part 4 becomesplastic and unites with the part 3 progressively from the contactingedge and forces any air or gases out of the useful part of the fusionline. I next finish the surface 8, see Fig. XIV, to fit the countersinkI of the blank 2.

As shown in Fig. XXIII the parts 3 and 4 may be fitted and fusedtogether before the diaphragms 5 are removed. This makes possible abetter line of fusion throughout the thickness of the contacting edgesof the parts.

After the parts 3 and 4 have been treated as described, I place thecomposite segment or button with the surface 8 in contact with thecountersink I, see Fig. XVIII, and place the assembled blanks on therefractory fusing block 9, see Fig. XIX, and apply heat to fuse thecomposite segment to the blank 2.

The parts 3 and 4 are. united edge to edge along the line l4, see Fig.XIII. The line of jointure I4 comprises the transverse upper portion [5,arouate fillets l6 at the outer extremities of the transverse portionl5; depending portions I! joined to the fillets I6 and substantiallyparallel; and fillets l8 connecting the depending portions H and theouter terminal portions 2!, which are substantially parallel to theportion l5. If desired the fillets 16 may be omitted and the portions I!may extend from the transverse portion l5 and the angle the portions llmake with the portion I5 will depend upon the. shape of the segmentdesired. The essential feature of the invention resides in the provisionof the button part 3 having the upper portion l5 and the terminatingportions "5 or I! with which the portion 20 may be aligned during theforming of the curve ID on the lens blank.

The transverse portion l5 and the fillets IS determine the shape of theupper portion of the finished segment. The depending portions I! whichtogether with the fillets [6 determine the width of the transverseportion and provide definite datum lines with respect to which the upperextremities of the lower circular portion 20 may be accurately alignedduring the abrading operations to obtain a feather edge along theportion 20 as shown in Figs. I and II. The fillet portions l8 insure. a.better fusion line between the parts and also make the parts easier tomold. The outer portions 2| provide a visible line, the length of whichmay be very readily seen by the operator in order to tell how the basecurve ID on the blank is being formed with respect to the reading button4 to form the lower circular portion 20. The portion 20 may be arcuatebut not necessarily circular, depending on whether or not thecountersink and curve In is spherical, torical or cylindrical.

After the composite blank has been made, as shown in Fig. XVII, thebutton or segment side is finished off to a spherical continuous opticalsurface I0, see Fig. II, as is usual in prior art practice. The surfaceof the countersink I being spherical and the surface being sphericalproduces the circular outline 20 of the lower part of the finishedsegment, see Fig. I, as it is the intersection of two sphericalsurfaces. During the formation of the optical surface H), the operatorwatches the visible portions 2| and adjusts the blank relative to theabrading apparatus so that the lengths of these lines 2| decrease inlength simultaneously until the upper edges of the circular portion 20aligns with the depending portions I! which are continuations of thefillets IS. The operator also takes note of the vertical dimension ofthe finished segment, and if after. the sides of the circular portionhave aligned with the portions II, the distance from the center of thetransverse portionl to the lo-wermost point on the portion 20 is greaterthan the predetermined dimension, the blank is adjusted relative to theabrading apparatus so that the greater grinding pressure is applied tothe lower part of the segment and thus cause the circular portion tomove upward but maintaining its radius constant. When the final desireddimension is reached, the upper end of the circular portion 20 will jointhe lower ends of the fillets it.

The circular portion 2!] will have a knife edge substantially fromfillet to fillet because the outline is produced by the intersection ofthe two spherical curves H! and the countersink while the transverseportion I5 and the fillets lfiwill have a cliff-type edge. The manner inwhich the relation of the curve i0 is being ground on the blank may becontrolled or varied in any manner well known in the prior art.

In the modification shown in Fig. XXII, the lower part of the readingsegment indicated at 24 does not have the transverse terminal portions2|. The important thing is to maintain the upper part of the readingportion 24 having the higher index of refraction against distortion.This is accomplished by the shape of the part 23 having the highermelting point. During the forming of the surface II], the surface isformed down until the upper portion of the circular outline 20 closes inand aligns with the fillets I6 due to the changing line of intersectionof the two spheres. The outline 20 will also have a knife edge for thesame reason. To finish the lens to prescription requirements, theopposite face is finished to the prescription surface II. It may beeither a spherical, toric or cylinder or in prismatic relation with thefirst surface.

Referring to Fig. XX, showing amodification of the invention, the parts3 and 4 of the button or segment are shown in place for fusion, the part4 being above the part 3 for the reasons set forth above. It will benoted that the part 4 contacts the part 3 at the point l2 substantiallyin the center of the dividing line, and also that there is a clearance13 between the parts on either side of this point. During fusion thepart 4 melts first and runs down toward the part 3, fusing from thepoint l2 outwardly on either side pushing out the air as it fuses andthus voiding air bubbles in the fused surfaces.

The finished lens has all the characteristics of the prior art lenses ofthis character as to, index of refraction, coefficient of expansion,coefficient of dispersion, color, melting points, oxidizing oranti-tarnishing effects, chemical compositions of the glasses and fusingcharacteristics, etc.

I have shown the invention applied to bifocal lenses. A trifocal ormultifocal lens may be made in the same way by making the part 3 ofdifferent index of refraction from the part 2 or by making the part 4 ofa plurality of pieces of glass of different indices of refraction fusedtogether in edge to edge relation with each other.

It will be understood that if the part 3 is the same index of refractionas the part 2, the part 3 will disappear on fusion, merging with thepart 2. If the glasses are of different index of refraction, the part 3will remain visible and a trifocal lens will be produced.

Where the piercing and the three part methods are used, a much largercountersink in the blank 2 is necessitated which requires more grinding,and also there is required more grinding over the button to bring it tothe finished condition, and unless an excessive amount of grinding isdone, the button will have a thick edge because the portion beyond thesegment has to be ground away before the segment is reached. It isdifficult to determine when the segment is reduced to a knife or featheredge throughout the lower portion of the segment as the contour shape ofthis portion is not produced by the intersection of two sphericalsurfaces as disclosed by this invention. The segments of such structuresare preshaped prior to the fusing and abrading operations and great caremust be taken during the abrading of the base' curve of the lens so thatthe said abrading is ceased just as the feather edge appears. Theposition of the base curve relative to the segment must also becarefully controlled so that the entire contour. of the lower portionwill be reduced to a feather edge simultaneously. These diflicultieshave been overcome by my method.

The parts 3 and 4 of the button have been particularly described asbeing formed by pressing, but it is to be clearly understood that I maygrind or form the parts in any manner well known in the art. The line ofjointure having fillets makes it particularly feasible to produce thecontacting edges by a forming tool. Likewise, the contacting surfacesmay be finished in any well known manner other than sandblasting asparticularly described and I do not wish it to be understood that myinvention is limited to sandblasting the edges.

If the parts 3 and 4 are formed by a forming tool instead of bypressing, the glass corresponding to the diaphragms 5 may not be left onduring the other operations on the button. The parts 3 and 4 may also befused together, as in Fig. XXIlI, before the diaphragms are taken off,since a better line of fusion would be possible throughout the line ofcontact the full thickness of the parts.

It is to be understood that although the parts of the segments have beendescribed as having specific shapes which are possibly of the greatestcommercial value, these shapes are only illustrative for the purposes ofclearly elucidating the invention. The invention primarily resides notonly in producing reading segments in bifocal or multifocal lenseshaving these specific shapes by a more eflicient and less expensivemethod, but also in producing other shapes of segments havingnoncontinuous contour lines by a less expensive method.

The broad concept of the invention contemplates the method of making areading segment for a bifocal or multifocal lens in which a portion ofthe noncontinuous contour of the final shape of the reading segment ispreformed and the remaining portion being formed by the intersection ofthe outer final surface of the lens blank with the surface of thecountersink; the preformed portion serving as guides or datum lines forcontrolling the size and shape of the portion of the contour formed bythe intersection of said surfaces.

The portion 15 has been described as substantially transverse and it isto be understood that this is intended to include a portion having longor short radius. The terminating portions l6 and I! may be curved orstraight. They are preferably straight because a greater tolerance maybe possible without producing a sharp intersection of the portion 20with the terminal portions l6 or H. In any event these terminal portionsform readily visible gauge lines for the operator during the formationof the surface Ill. Although the countersink and base curve In are setforth as preferably being spherical, they may be made to any otherdesired curvature.

From the foregoing it will be seen that I have provided improved meansfor obtaining all the objects and advantages of the invention includinga greatly reduced cost of production of lens blanks for lenses of thischaracter. By this invention I have provided a novel lens blank for abifocal or multifocal lens and method of making same, having a readingsegment with a portion thereof having a preformed noncontinuouscliff-type edge and the remaining portion having a feather edge formedby the intersection of the countersink curve and the base curve on theblank. Thus, the preformed portion provides ready gauge means for theoperator in order to produce an accurate lens. A lens made by my methodwill also be more optically perfect because where the piercing or threepart methods are used the segment is entirely surrounded by the walls ofthe button, proper expansion and contraction and annealing cannot takeplace and strains are set up producing a warped condition destroying thetrue optical surface.

Having described my invention, I claim:

1. A multifocal lens blank for producing a lens having a reading segmentformed with a circular lower portion and a transverse upper portionjoined adjacent its ends with portions meeting the ends of the circularportion, comprising a major portion of glass of one index of refractionwith a spherical countersink recess therein and a minor portion securedin said recess, said minor portion comprising two pieces of glass ofdiflferent indices of refraction having portions abutted edge to edgetransversely of the blank, one of said transverse edges having a centraltransverse section, deflected sections intermediate the ends thereofextending at an angle to and to one side of said central section andterminal oifset end sections spaced from the central transverse section,said deflected sections forming portions of the side contours of thefinished segment of the lens and being adapted, in the finished lens, tolie within the line of a circle generated by the intersection of thespherical surface of the countersink recess and a spherical surfaceformed on the segment side of the blank, said circular line beingadapted to produce the lower circular portion of the segment of thefinished lens with portions of the deflected sections meeting the endsof the lower circular portion and providing means for joining said endswith the ends of the central transverse portion to complete the contourof the segment, said terminal oifset end sections located beyond saidcircle being adapted to disappear when the said spherical surface isgenerated on the segment side of the blank.

2. A multifocal lens blank for producing a lens having a reading segmentformed with a circular lower portion and a transverse upper portionjoined adjacent its ends with portions meeting the ends of the circularportion, comprising a major portion of glass of one index of refractionwith a spherical countersink recess therein and a minor portion securedin said recess, said minor portion comprising two pieces of glass ofdifferent indices of refraction having portions abutted edge to edgetransversely of the blank, one of said transverse edges having a centraltransverse section, deflected sections intermediate the ends thereofextending at an angle to and to one side of said central section andterminal offset end sections spaced from the central transverse section,said deflected sections forming portions of the side contours of thefinished segment of the lens and being .adapted, in the finished lens,to lie within the line of a circle generated by the intersection of thespherical surface of the countersink recess and a spherical surfaceformed on the segment side of the blank, said circular line beingadapted to produce the lower circular portion of the segment of thefinished lens with portions of the deflected sections meeting the endsof the lower circular portion and providing means for joining said endswith the ends of the central transverse portion to complete the contourof the segment, said terminal offset end sections located beyond saidcircle being adapted to disappear when the said spherical surface isgenerated on the segment side of the blank, the height of the segmentbeing controlled by the relative positions of the axes of the sphericalsurface of the countersink and the spherical surface to be formed on thesegment side of the blank and by the depth to which said last namedsurface is to be formedv 3. The method of making a multifocal lens blankhaving a reading segment having a transverse-upper portion and acircular portion on the lower side, comprising forming a curvedcountersink in a major lens blank, forming a segment button of twopieces of glass of different indices of refraction with male and femalelines of joinder, one of which has a central transverse section,deflected sections controlling the width of the finished reading segmentof the lens and terminal offset end sections spaced from the centraltransverse section, securing said two pieces of glass together alongsaid lines of joinder, securing said button in said countersink, andforming an optical surface on the segment side of the composite fusedblank to such a depth as to cause the offset transverse end sections toclose in until the said surface intersects the curve of the countersinkand forms a circular contour throughout the lower portion of the segmentand continuing the abrading of said surface until the lower circularcontour approaches and meets the deflected end sections of the centraltransverse section whereby the said offset transverse end sections willdisappear and the deflected end sections will form portions of the sidecontours of the finished reading segment of the blank.

1. The method of making a multifocal lens blank having a reading segmenthaving a transverse upper portion and a circular portion on the lowerside, comprising forming a curved countersink in a major lens blank,forming a segment button of two pieces of glass of different indices ofrefraction with male and female lines of joinder, one of which has acentral transverse section, deflected sections controlling the width ofthe finished reading segment of the lens joined with the transversesection by curved fillets and terminal offset end sections spaced fromthe central transverse section, securing said two pieces of glasstogether along said lines of joinder, securing said button in saidcountersink, and forming an optical surface on the segment side of thecomposite fused blank to such a depth as to cause the offset transverseend sections to close in until the said surface intersects the curve ofthe countersink and forms a circular contour throughout the lowerportion of the segment and continuing the abrading of said surface untilthe lower circular contour approaches and meets the deflected endsections of the central transverse section whereby the said offsettransverse end sections will disappear and the deflected end sectionswill form portions pieces of glass together of the side contours of thefinished reading segment of the blank.

5. The method of making a multifocal lens having a reading segmenthaving a transverse upper portion and a circular portion on the lowerside, comprising forming a curved countersink in a major lens blank,forming a segment button of two pieces of glass of different indices ofrefraction with male and female lines of joinder, one of which has acentral transverse section, reflected sections controlling the width ofthe finished reading segment of the lens and terminal offset endsections spaced from the central transverse section, securing said twopieces of glass together along said lines of joinder, securing saidbutton in said countersink, and forming an optical surface on thesegment side of the composite fused blank to such a depth as to causethe offset transverse end sections to close in until the said surfaceintersects the curve of the countersink and forms a circular throughoutthe lower portion of the segment and continuing the abrading of saidsurface until the lower circular contour approaches and meets thedeflected end sections of the central transverse section whereby thesaid offset transverse'end sections will disappear and the deflected endsections will form portions of the side contours of the finished readingsegmentof the blank and finishing the opposite side of the blank to acontinuous optical surface.

6. The method of making a multifocal lens having a reading segmenthaving a transverse upper portion and a circular portion on the lowerside, comprising forming a curved countersink in a major lens blank,forming a segment button of two pieces of glass of different indices ofrefraction with male and female lines of joinder, one of which has acentral transverse section, deflected sections controlling the width ofthe finished reading segment of the lens joined with the transversesection by curved fillets and terminal offset end sections spaced fromthe central transverse section, securing said two pieces of glasstogether along said lines of joinder, securing said button in saidcountersink, forming an optical surface on the segment side of thecomposite fused blank to such a depth as to cause the offset transverseend sections to close in until the said surface intersects the curve ofthe countersink and forms a circular contour throughout the lowerportion of the segment and continuing the abrading of said surface untilthe lower circular contour approaches and meets the deflected endsections of the central transverse section whereby the said offsettransverse end sections will disappear and the deflected end sectionswill form portions of the side contours of the finished reading segmentof the blank, and finishing the opposite side of the blank to acontinuous optical surface.

7. The method of making a multifocal lens having a reading segmenthaving a transverse upper portion and a circular portion on the lowerside, comprising forming a curved countersink in a major lens blank,forming a segment button of two pieces of glass of different indices ofrefraction with male and female lines of joinder, one of which has acentral transverse section, deflected sections controlling the width ofthe finished reading segment of the lens and terminal offset endsections spaced from the central transverse section, securing said twoalong said lines of joinder, securing said button in said countersink,and forming an optical surface on the segment contour side of thecomposite fused blank to such a depth as to cause the oiTset transverseend sections to close in until the said surface intersects the curve ofthe countersink and forms a. circular contour throughout the lowerportion of the segment and continuing the abrading of said surface untilthe lower circular contour approaches and meets the deflected endsections of the central transverse section whereby the said oftsettransverse end sections will disappear and the deflected end sectionswill form portions of the side contours of the finished reading segmentof the blank and the remaining lower edge of the segment will have aknife-like edge, and finishing the opposite side of the blank to acontinuous optical surface.

FAY D. KINNEY.

